Is Relational Quantum Mechanics Truly Profound or Simply Confusing?

[jfy4]

Hi,

I was looking through Rovelli's Relational QM paper

http://arxiv.org/abs/quant-ph/9609002"

and Unfortunatly I didn't find the initial set-up of the story compelling. In this set up, there is a system, S, and an observer O. S can be in one of two states $|\psi\rangle =\alpha |1\rangle + \beta |2\rangle$. Assume that for a specific measurement at time $t=t_2$ O observers S in state $|1\rangle$. Now let a new observer, P, describe the S-O system quantum mechanically. Then without interacting with the S-O system, it is described by P as $\alpha |1\rangle\otimes |O1\rangle + \beta |2\rangle \otimes |O2\rangle$ where O2 and O1 indicate that O has interacted with S and observed result 1 or 2 respectively. Then from this Rovelli states,

At time $t_2$, in the O description, the system S is in the state |1⟩ and the quantity q has value 1. According to the P description, S is not in the state |1⟩ and the hand of the measuring apparatus does not indicate ‘1’.

and then that

In quantum mechanics different observers may give different accounts of the same sequence of events.

But to me this conclusion and argument aren't particularly compelling. To me this says that O has a value for S, say 1, but P doesn't have a particular value for the S-O system. That's okay with me, since P never made a measurement in the first place, I'd certainly not expect P to have a value at hand. This seems just like if Sally and Oscar have a box in front of them with two balls, red and green, and Oscar picks a ball at random and looks to see what it is, but Sally can't check either the box or Oscar. Then Oscar has a value for the ball color, but Sally doesn't know the ball color, or what Oscar knows as the ball color.

I don't see a problem with this... This seems completely normal and non-exclusive. Can someone help me see the profoundness in this example.

Thanks,

 

[eljose79]

I understand your confusion and hesitation in finding Rovelli's example compelling. However, I believe that the key point here is the concept of observer-dependent reality in quantum mechanics. This means that the reality of a system is not determined until it is observed by an observer, and different observers can have different perceptions of the same reality.

In Rovelli's example, the observer O measures the state of system S and finds it to be in state |1⟩, while the observer P, who has not interacted with the system, describes it as being in a superposition of states. This illustrates the idea that reality is not fixed and objective, but rather dependent on the observer and their interactions with the system.

The profoundness of this example lies in the fact that it challenges our traditional understanding of reality and suggests that our perception of it is not a complete representation of the truth. It also raises questions about the role of consciousness in shaping reality, as the act of observation is often linked to consciousness.

Furthermore, this example also has implications in the field of quantum computing and quantum information, where the concept of observer-dependent reality is being explored for potential applications.

I hope this helps you see the significance of Rovelli's example and the deeper implications it has in the field of quantum mechanics. Feel free to ask any further questions or for clarification.